The main standard defined by the IEEE 802.16 task group includes IEEE 802.16-2004 called fixed WiMAX and IEEE 802.16e-2005 (16e) called mobile WiMAX. The IEEE 802.16e-2005 has been finally approved from the IEEE on December of 2005 as the standard. The standard based on mobile WiMAX of a current version includes IEEE 802.16-2004, IEEE 802.16e-2005 (this document includes Corrigenda of IEEE 802.16-2004), and IEEE 802.16-2004/Corrigenda2/D4. Currently, standardization of IEEE 802.16m (16m) for mobile WiMAX of next version is in progress by TGm within the IEEE 802.16 task group.
In the IEEE 802.16e, a ranging procedure is used for various purposes of use. In more detail, the ranging procedure is used for four purposes of use as follows: initial ranging, handover ranging, periodic ranging and bandwidth request ranging. The initial ranging is used for uplink time synchronization (that is, time and frequency synchronization) if a user equipment tries to initially enter a network. The handover ranging is used for initial synchronization with a target base station if access is changed from a source base station to the target base station. The periodic ranging is used to update uplink synchronization periodically. The bandwidth request ranging is used to allow a user equipment to request a base station of uplink resources.